#Kotlin notes by theam.
This notes are taken in order to serve as a study guide for Kotlin to theam developers
- Kotlin official reference
- [Kotlin for Android Developers] (https://leanpub.com/kotlin-for-android-developers)
- Kotlin in Action
- You can do better with Kotlin by Svetlana Isakova
##Main features
- More expresive than Java
- Null Safe (No more fails safe conditions in our code, No more NullPointerException)
- Functional (Uses many concepts of a functional language)
- You can create extension functions to extend any class
- It's highly interoperable, you can use your favourite Java Libraries
- Inmutability (val/var keywords)
###Some examples
Sample definition of a POJO in Kotlin
data class Artist(
var id: Long,
var name: String,
var url: String,
var mbid: String)
data keyword provides toString, equals, hashCode and copy by default
Getters and setters
public class Person {
var name: String = ""
// We'll need to use field reserved word
// inside property accesors
get() = field.toUpperCase()
set(value) {
field = "Name: $value"
}
}
Nullable
The following code will not compile
var name: String
name = null
Instead will need to use ? after type declaration to indicates that a value could be null
var name: String?
name = null
In Java we have tons of code like this (let's supposed we've an artist object and we want to print his info):
if (artist != null) {
return artist.print()
}
We could rewrite the above code removing the condition and using a safe method call using ?
return artist?.print()
Extension functions
Fo exmaple let's extend our Context in Android to provided a nice Toastmessage to our Activities, Fragments or whatever
fun Context.toast(message:CharSequence, duration: Int = Toast.LENGTH_SORT) {
Toast.makeText(this, message, duration).show()
}
Then in our activities we can call this method directly
toast("Hello World!")
toast("Hello World!", Toast.LENGTH_LONG)
##Kotlin and Android